When I try to fetch Order from Payment with lazy loading I receive empty Order object with null properties. If I use eager fetching Order object is valid.
SQL generated for lazy loading seems to be valid, so I suppose the problem is in mapping result to the object. At the same time lazy loading works fine with 2.0.6 version.

I don't think its supported to use a non primary id for foreign key matching. I cant tell for sure though since i wasnt responsible to design this part of the Doctrine code. I would strongly suggest not to do this.